1. Field of the Disclosure
The present disclosure relates generally to spark plugs and, more particularly, to methods for applying coatings to insulators of spark plugs to minimize fouling.
2. Description of the Background
Spark plugs used as igniters in internal combustion engines are subjected to a condition known as “fouling.” Over time, carbon and other products of combustion can accumulate on the spark plug, including the surface of an insulator tip of the spark plug, which is typically positioned at or near a boundary of unmixed fuel, or at or near the center electrode tip. The products of combustion of a gasoline engine include particles of fuel additives such as Methylcyclopentadienyl Manganese Tricarbonyl (MMT) and Ferrocene, which are often added to gasoline as an octane enhancement. Normally, accumulated soot that is located near the spark point of the spark plug would be burned off from the heat of the combustion process. However, because the exposed surface of the insulator tip may not be located in or about a spark gap between the center electrode tip and ground electrode, accumulated combustion soot along the insulator tip may not be burned off. If significant amounts of these combustion products accumulate, the spark may not properly form between the center and ground electrodes. More particularly, the accumulated combustion soot creates an electrical short circuit such that the electrical charge from the center electrode travels across the surface of the insulator and back to the outer metal shell instead of across the spark gap to the ground electrode. This process is called “fouling.”
As noted above, MMT and/or other additives have been added to gasoline or fuel to increase the octane numbers instead of using a more expensive refining process. MMT added to the fuel generates conductive combustion residual that deposit on the internal surfaces of the combustion engine, including the insulator of a spark plug that extends into the engine combustion chamber. It has been found that MMT deposits on a surface of the spark plug insulator significantly reduce the resistivity of the spark plug insulator and may cause instances of side-firing or misfiring during ignition events. In turn, the MMT deposits have dramatically reduced the useful life of spark plugs, leading to high costs due to frequent replacement of spark plugs. MMT deposits may also reduce fuel mileage and/or increase hydrocarbon emissions. While some methods have been developed to reduce or minimize MMT deposits, the current methods have their challenges.